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LTR Retrotransposons

LTR Retrotransposons

LTR retrotransposons are class I transposable elements with long terminal repeats flanking an internal coding region. These elements are less abundant in mammals compared to other class I transposable elements. About 8 percent of human genomic DNA comprises LTR retrotransposons. Some of the common examples of LTR retrotransposons are Ty elements in yeast and Copia elements in Drosophila.
The internal coding region of LTR retrotransposons and their mechanism of transposition closely resembles a...

Non-LTR Retrotransposons

Non-LTR Retrotransposons

As the name suggests, non-LTR retrotransposons lack the long terminal repeats characteristic of the LTR retrotransposons. Additionally, both LTR and non-LTR retrotransposons use distinct mechanisms of mobilization. Non-LTR retrotransposons are further divided into two classes - Long interspersed nuclear elements (LINEs) and short interspersed nuclear elements (SINEs), both of which occur abundantly in most mammals, including humans. Some of the active non-LTR retrotransposons in humans are L1...

Retroviruses

Retroviruses

Retroviruses and retrotransposons both insert copies of their genetic elements into the genome of the host cell. Thus, the viral genes are passed on when the host genome is replicated or translated. A typical retroviral DNA sequence contains 3-4 genes that encode the different proteins required for its structural assembly and function as a molecular parasite. This DNA is transcribed into a single mRNA, which is very similar in structure to conventional mRNAs, i.e., it is capped at the 5’...

Retrovirus Life Cycles

Retrovirus Life Cycles

Retroviruses have a single-stranded RNA genome that undergoes a special form of replication. Once the retrovirus has entered the host cell, an enzyme called reverse transcriptase synthesizes double-stranded DNA from the retroviral RNA genome. This DNA copy of the genome is then integrated into the host’s genome inside the nucleus via an enzyme called integrase. Consequently, the retroviral genome is transcribed into RNA whenever the host’s genome is transcribed, allowing the retrovirus to...

Mechanisms of Retrovirus-induced Cancers

Mechanisms of Retrovirus-induced Cancers

Retroviruses are RNA viruses that have been shown to cause cancers in diverse species, including chickens, mice, cats, and monkeys. The RNA genomes of these viruses are first reverse-transcribed into single and then double-stranded DNA (dsDNA) copies. This dsDNA called proviral DNA then integrates into the host genome. Subsequently, the host cell transcribes the proviral DNA in concert with the chromosomal DNA. This leads to the production of viral RNA and proteins that assemble at the host...

Size and Structure of Viral Genomes

Size and Structure of Viral Genomes

Viral genomes exhibit remarkable diversity in size, structure, and composition, influencing their replication strategies and interactions with host cells. These genomes consist of either DNA or RNA and may be linear or circular. Additionally, they can be single-stranded or double-stranded, with each configuration affecting how the virus propagates within a host. RNA viruses, for instance, generally have smaller genomes than DNA viruses, a factor that contributes to their high mutation rates and...

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Related Experiment Video

Updated: Jul 14, 2026

Mouse Models of Epididymitis Induced by Pathogen-Associated Molecular Patterns

Mouse Models of Epididymitis Induced by Pathogen-Associated Molecular Patterns

Published on: December 12, 2025

Endogenous retrovirus expression in testis and epididymis.

R C Crowell¹, A A Kiessling

¹Laboratory of Reproductive Biology, Department of Surgery, Harvard Medical School, 4 Blackfan Circle, Boston, MA 02115, USA.

Biochemical Society Transactions

|May 22, 2007

Summary

Endogenous retroviruses (ERVs) show differential expression in male reproductive tissues. This study detected six human ERV families in the epididymis and three in the testis, suggesting a link to cellular differentiation.

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Microarray-based Identification of Individual HERV Loci Expression: Application to Biomarker Discovery in Prostate Cancer

Microarray-based Identification of Individual HERV Loci Expression: Application to Biomarker Discovery in Prostate Cancer

Published on: November 2, 2013

Area of Science:

Genomics and Molecular Biology
Reproductive Biology
Retroviral Research

Background:

Endogenous retroviruses (ERVs) constitute a significant portion (8-10%) of mammalian genomes.
While ERVs are known to be differentially expressed in various tissues, their biological roles remain largely undetermined.
Previous studies indicated high ERV expression in mouse epididymis but not testis, and limited human ERV (HERV) expression data.

Purpose of the Study:

To investigate the expression patterns of multiple human endogenous retrovirus (HERV) families in the human testis and epididymis.
To explore the relationship between cellular differentiation in these tissues and HERV expression.
To identify HERVs potentially interacting with sperm.

Main Methods:

Utilized degenerate primers targeting conserved reverse transcriptase regions specific to nine distinct HERV families.
Analyzed HERV expression in human epididymis and testis samples.

Main Results:

Detected expression of six HERV families in the epididymis.
Detected expression of three HERV families in the testis.
Observed differential HERV expression between the epididymis and testis.

Conclusions:

Differential HERV expression in the epididymis and testis may correlate with the distinct cellular differentiation states of these tissues.
The findings provide a foundation for understanding how cellular differentiation influences HERV expression in reproductive organs.
This research highlights specific HERVs that are consistently exposed to sperm.